Today, large parts of milking related operations have been automated and many farmers utilize automated milking system for milking their milking animals. A prerequisite for implementing such automation is a vacuum regulation system for creating and regulating vacuum within the milking system.
Generally, there are different issues to take into consideration when designing a vacuum regulation system for a milking system. An excessive vacuum level may injure the animals being milked, while on the other hand a too low vacuum level may slow down the milking related operations. Further, it is desirable to keep the vacuum level of a milking system at a constant level during certain operations, without unnecessary fluctuations of the vacuum level.
It is desirable to keep the energy consumption at a lowest level possible in the milking system. The vacuum regulation system of a typical dairy farm consumes a large part of the total amount of electricity used and the vacuum regulation system should thus be made as efficient as possible.
The vacuum regulation system typically comprises a vacuum pump, which is chosen so as to be able to remove air from within the milking system to meet a required maximum vacuum level and air demand within the milking system. If a single vacuum pump is not enough to meet the requirements, then two or more vacuum pumps may be installed. The vacuum pumps may be arranged to provide vacuum in different parts of the milking system. The vacuum regulation system further typically comprises a control device to regulate the speed of the vacuum pumps, and thereby the amount of air being removed from the milking system and/or to regulate valves for keeping the vacuum level at a desired level.
An example of a vacuum regulation system comprising variable speed vacuum pumps is disclosed in the International patent publication WO 2006/006906, assigned to the same applicant as the present application. If the vacuum requirement within the milking system is such that the capacity of a first vacuum pump is not enough, then the speed of the first vacuum pump is set to a fixed speed, while a second vacuum pump is started. The vacuum level in the milking system is then controlled by means of the speed of the second vacuum pump.
There are difficulties involved when controlling two or more vacuum pumps simultaneously. For example, it may be difficult to keep the vacuum level at a constant level. This is especially the case when the amount of air required to be removed from the milking system is rather low and the vacuum pumps are therefore run at a low speed. There is also a danger of overheating the vacuum pumps.
In view of the above it would be desirable to provide an improved method for controlling a vacuum level within a milking system.